Note: Descriptions are shown in the official language in which they were submitted.
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fOIICf-1 CONTAINERS AND FIL~1S THEI2EI'OR
FIELD OF THE INVENTION
This invention relates to multi-layer films sui.t:able for making
pouches that can be sealed using radio frequency energy, and in particular
to pouches that contain liquids or pastes and which have at least a partial
transmissivity of oxygen and aromatic substances.
BACKGROUND OF. THE INVENTION
There is a continuing effort to decrease the weight mass of material
used in packaging. As a part of this effort, substances that have been
sold in bottles are now being sold in film pouch containers. This reduces
the packaging weight to less than half of that of a bottle. There can be
an additional savings if the liquid substance is concentrated prior to film
packaging. In this way, the amount of film packaging required can be
further reduced since the diluent is added at the time of use. However, a
rya,
film must have specific properties in order to be effectively used for
packaging. This is particularly the case when the film package is to be
formed and/or sealed using radio frequency (RF) energy techniques. In RF
sealing techniques, RF energy is used to soften the film sufficiently so
that the film can be welded. This is an effective sealing technique since
the two layers of film that are to form the pouch are heated to similar
temperatures and can be welded. At the point of sufficient softening, but
prior to any flowing of the film material, the two layers become welded.
This provides for significant advantages over techniques that use adhesives
or the heating of the film by conduction, i.e., through contact with a
heated plate. It .is also the case that RF energy provides for a more
unifarm heating and thus produces good seals.
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Although RF energy provides for good seals, there are
certain requirements with regard to the use of RF energy. The
film must be capable of being heated using RF energy. That is,
it must be able to be heated to near melt through contact with
RF energy having a frequency of about 10 MHz (Megahertz) to 50
MHz. This is the frequency range most used for heating
polymeric materials. Not all polymeric films can be
effectively heated to produce good seals using RF energy. The
plastic film used in the sealing layer must be bysular for RF
sensitivity.
The films will also require other characteristics
dependent at least in part on the substance that is contained
in the pouch made from the film. It has been found that when a
film is to contain a bleach that the film must have a
transmissivity for oxygen since oxygen is evolved during the
storage of bleach pouches. If this oxygen cannot be dissipated
through the pouch wall, pressure will build-up in the pouches
to the point that the pouches could possibly rupture. If this
occurs, there would be a loss of product and possible damage to
the surrounding area. In addition, it is desirable with many
substances to have some of the aroma of the substance contained
in the pouch be transmitted to the exterior. This provides a
way to acquaint the customer with the fragrance of the product.
Consequently, it is desirable for the film to have a partial
transmissivity for fragrances.
BRIEF SUMMARY OF THE INVENTION
The invention provides a sheet of material for
producing pouches for containing substances consisting of three
adjacent film layers of an inner barrier layer and two exterior
seal layers, the barrier layer being a polyolefin and the seal
layers being ethylene vinyl acetate copolymer layers having an
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average vinyl acetate content of at least about 18 percent by
weight, said adjacent film layers having a slip agent content
of about 500 to 3,000 parts per million, at least a partial
transmissivity to fragrances, a transmissivity to oxygen of at
least about 600 cm3/m2/day/bar, the combined adjacent film
layers being of an age since being made of about 2 to 24 weeks
whereby said slip agent has not significantly migrated to
exterior surfaces of said combined film layers and whereby said
seal layers can be welded using radio frequency welding to
produce pouches. The barrier layer provides the primary
containment layer and is the primary strength layer. The seal
layers will readily absorb RF energy, soften and be weldable in
the softened state. The outer layer should also be printable.
In addition to conveying information, the print will function
as a slip agent during pouch formation from the film. -Further,
in order to form pouches having high strength seals using RF
energy, the film should preferably be used to form pouches
within about 4 weeks to 20 weeks after film manufacture.
The invention also provides a pouch containing a
substance comprising a sheet of material sealed to form a
closed volume and consisting of three adjacent film layers of
an inner barrier layer and two exterior seal layers, the
barrier layers being a polyolefin and the seal layers being
ethylene vinyl acetate copolymer layers having an average vinyl
acetate content of at least about 18 percent by weight, said
adjacent film layers having a slip agent content of about 500
to 3,000 parts per million, at least a partial transmissivity
to fragrances, a transmissivity to oxygen of at least about 600
cm3/m2/day/bar, the combined adjacent film layers being of an
age since being made of about 2 to 24 weeks whereby said slip
agent has not significantly migrated to exterior surfaces of
said adjacent film layers and whereby said seal layers can be
welded using radio frequency welding to produce pouches.
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The invention further provides a method for forming a
pouch comprising: forming a multi-layer film consisting of
three adjacent film layers of an inner barrier layer and two
exterior seal layers, the barrier layer being a polyolefin and
the seal layers being ethylene vinyl acetate copolymer layers
having an average vinyl acetate content of at least 18 percent
by weight, said adjacent film layers having a slip agent
content of 500 to 3,000 parts per million, a transmissivity to
fragrances of 1 to 25 weight percent of the fragrance content
l0 during a 90 day period, a transmissivity to oxygen of at least
600 cm3/m2/day/bar; permitting said multi-layer film to age for
a period of 2 to 24 weeks whereby said slip agent has not
significantly migrated 'to exterior surfaces of said combined
film layers; superimposing parts of a sheet of multi-layer
material so that the overlapping parts form the edges of the
pouch; and sealing the :latter by welding the overlapping seal
layers using radio frequency energy. The ethylene-vinyl
acetate layers of the sheet should preferably have an average
vinyl acetate content of at least about 20 percent by weight.
Thus, one ethylene-viny:L acetate layer can have a vinyl acetate
content of less than 18 or 20 percent by weight as long as the
other layer has a sufficiently high enough vinyl acetate
content so that the average of both layers is at least about 18
percent by weight and preferably 20 percent by weight. The
film has a thickness of about 125 microns to 500 microns, and
preferably about 200 microns to 300 microns. The barrier layer
has a thickness of about 25 microns to 100 microns, and
preferably about 40 microns to 75 microns. The seal layer has
a thickness of about 50 microns to 200 microns and preferably
about 75 microns to 150 microns.
In addition to'the foregoing, the film should have an
oxygen txansmissivity of preferably at least about 1000
cm3/m2/day/bar. The transmissivity for fragrances should be
about 1 to 25 weight percent of the fragrance content during a
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90 day period and preferably about 3 to 15 weight percent of
the fragrance content during a 90 day period. In this way,
oxygen produced in the partial degradation of a substance such
as bleach can be removed from the pouch and
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~a48949
the fragrance of the product can be sensed by persons at the tirn~ of
purchase.
BRIEF DESCRIPTION OF THE DRAWING
The Figure is a rear elevation of a pouch container having a spout.
DETAILED DESCRIPTION OF THE INVENTION
Polymer films are effective in many packaging uses. These polymer
films can either be a single layer or multi-layer films. In many
instances, a multi-layer film will have to be used since the film will have
to have particular characteristics. Sometimes,'.the characteristics are
dictated by the package design and the substance being packaged. There
must be a computability. The primary contained substance usually should
not permeate through the polymer film. Strong seals should be formable.
These are just some of the characteristics. In addition, when a bleach is
being packaged, the film should have an oxygen transmissivity_ It is also
desirable in many instances if some of the fragrance of the product can
permeate through the film. This permits the consumer to determine whether
the fragrance of a product is acceptable.
It has been found that household products such as bleaches and fabric
softeners, can be packaged in film pouches that are comprised of at least
one barrier layer and of at least one seal layer. The barrier layer is
preferably a polyolefin such as polyethylene or polypropylene. The
polyethylene can be a high or low density polyethylene. The seal layer is
preferably ethylene-vinyl acetate, and most preferably ethylene-vinyl
acetate wherein the average vinyl acetate content is at least about 18
percent by weight and preferably at least about 20 percent by weight.
Also, in a preferred construction, the film has three layers. These
comprise a polyethylene layer with an ethylene-vinylacetate layer on each
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side. The polyethylene layer. serves as a barrier layer and provides
strength to tho film.
The film has a thickness of about 125 to 500 microns, and preferably
about 200 to 300 microns. The barrier polyethylene layer has a thickness
of about 25 microns to 100 microns, and preferably about 40 microns to 75
microns. The seal ethylene-vinylacetate layers have a thickness of about
50 microns to 200 microns, and preferably about 75 microns to 150 microns.
The ethylene-vinylacetate layers need not have the same thickness.
However, in many instances, the same thickness will be used.
The film should have an oxygen permeability of at least about 600
cm3/m2/day/bar and preferably at least about 1000 cm'/mz/day/bar. This is
particularly important in the packaging of bleach containing products which
evolve oxygen which must be removed as it is evolved in order to prevent
the rupture of the package. It is also a factor that the film have a
transmissivity for fragrances. It is desirable that the fragrance of the
household product be detected outside of the package. In this regard, the
film should be able to transmit about 1 to 25 weight percent of the
fragrance, and preferably about 3 to 15 weight percent of the fragrance
during a 90 day period. However, since the fragrance is in the product to
enhance the product during its use, the majority of the fragrance should
remain in the product and not be transmitted through the film.
In addition, in order to effect good RF sealing the film should be
within an age since manufacture of about 2 to 24 weeks, and preferably
about 4 to 20 weeks. This in an age that will result in maximum RF sealing
of the film. It has been found that films have a period after manufacture
wherein maximum strength RF seals can be produced. In thi:~ regard, pouches
and other containers should be formed during this period.
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'.Phe tame window when the film can be sealed most readi.Ly wi7.1 depend
to a large degree on 1=he amount of slip agent that has been added to Lhe
film. The amount of slip agent, in the present films will range from about
500 to 3,000 parts per million (ppm) of film resin. 'rhe slip agent i.s
usually a wax, and preferably an amide wax. The roll tension on the film
(tension of the film on the spool) will also affect the migration of the
slip agent to the exterior of the film. It is the migration of the slip
agent to the exterior surfaces of the film that results in poor RF sealing.
When a film is wound at higher tensions on a spool there is less migration
of the slip agent to the surface of the film. It stays to a large degree
locked in the film. However, it becomes free to migrate when the film is
unwound for various operations, such as printing and slitting.
A film will have a time window of usage in RF sealing depending
primarily on the slip agent content of the film and the time at the initial
winding tension (T~) and the time after unwinding for conducting one or
more operations such as printing and sliting (T2). Due to the stability of
the film at the initial winding tension T1 will be fairly long. The time
at TZ will be less than that at T'' since there is a greater migration of
slip agent from the film during TZ. The time window for use (T''+T2) will
be about 2 to 24 weeks with T2 being at least about 2 weeks to about 6
weeks. The time window for any particular film can be determined only by
testing of the film over a period of time.
The RF sealing is usually conducted~at frequency levels of about 10
megahertz (MHz) to 50 MHz and preferably 7.3.56 t4Hz, 27.12 MHz or 40.68 MHz.
Of these three frequencies, 27.12 ME3z is preferred. Sufficient energy is
used to quickly soften the ethylene-vinylacetate layers so that these
layers can be quickly welded to form a seal..
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'Phe f il.m package can bc: preformed and then filled or can be formed and
filled in a continuous operation. Those :latter techniques are known as
form/fill techniques.
Bleach is an aqueous solution of sodium hypochlorite. It; is sold in
d.ilutions of about 5 to 12 percent by weight sodium hypochlorite. The
remainder is primarily water but may include additives such as
preservatives, surfactants and perfumes. The film pouches in which the
bleach is pacl~aged ranges from 100 cc. to 500 cc. packages. A useful size
is 250 cc. It is also preferred that the film packages have a spout on the
upper end, the spout being in the form of a beak. Such a spout makes it
easier for the consumer to safely use the bleach or other household product
that is the subject of the packaging. A suitable package of this type is
shown in Figure 1. In this embodiment, there is shown a film package 10
having a longitudinal RF seal 12 on rear side 11. The bottom edge has an
RF seal 13 and the top edge an RF seal 14. This film package has a spout
15 which has been formed into the package. Seal 16 seals the pouch in the
area of the spout. This spout resembles a beak. This is a preferred
packaging. These concepts can be incorporated into other packaging.
The foregoing sets out a preferred embodiment of the present
invention. Modifications and variations can be made to suit particular
purposes. However, such modifications and variations would constitute a
practice of the present invention.
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